The present invention relates to display devices for characters in rows displayed from an electric control signal and more specifically display devices in which the inscribable material reacts optically with an electric field during a thermal cycle incorporating a heating phase and a cooling phase under field.
The invention more particularly applies to display devices having a matrix arrangement with a liquid crystal layer in the smectic phase.
A device of this type is described in French patent application 80 26544 entitled "Control device for a display screen and display screen controlled by this device",filed on Dec. 15th 1980, which was published on June 18, 1982 under the U.S. Pat. No. 2, 496,309. (The corresponding U.S. patent issued from U.S. Ser. No. 328,497 filed Dec. 8, 1981 as U.S. Pat. No. 4,427,997.) The proposed device makes it possible to considerably reduce the number of electronic external control systems by multiplexing the control channels, whilst retaining a high definition for the display screen.
The aforementioned patent application describes a matrix control display device comprising a layer of material which can be inscribed by a mixed thermal and electrical effect. According to this application, two crossed networks of conductors define a matrix arrangement of display points. One of the networks consists of heating elements for temporarily raising the temperature of the inscribable material layer. The other network cooperates with the first network for locally exposing the layer to electric control fields. The system arranges the N lines of a screen into .sqroot.N groups of lines supplied at each of their ends by .sqroot.N control devices functioning sequentially, as shown in FIG. 3 of the above-noted U.S. Pat. No. 4,427,997. Such an arrangement leads to a minimum number of electronic heating systems but from the standpoint of the interconnections to be provided it is necessary to have a relatively large number of insulated crossings. Moreover, the length of the heating strips can lead to significant voltage drops, which is not really suitable for a control by low voltage electronic components.